How to Set Stairs

Wider stairs need additional stringers to ensure that the steps are sturdy.

When building stairs, the process of setting stairs consists of installing the notched stringers at the correct angle. Stringers for interior stairs install between the floor and the edge of an upper landing. With exterior stairs, stringers install between a concrete footing and the edge of a deck or porch. Regardless of the application, it’s important to set stairs so that the steps are level and the entire run of steps is uniform. For longer runs that have longer stringers, the job is easier with the help of an assistant.

1

Determine the height where the upper ends of the stringers attach to the floor joist at the edge of a landing, deck or porch. Measure the thickness of a stair tread and note the measurement.

2

Work from a stepladder, if necessary, and measure down from the top of the subfloor or deck and mark the face of the joist at the thickness of the tread with a carpenter's pencil. Use a 4-foot level as a guide to mark a level, horizontal line across the face of the joist at the tread mark.

3

Determine the width of the stairs based on dimensions in a stair plan or personal preference. Deduct the desired overhang of the treads at both sides of the stairs to determine the distance between the stringers. Typically, interior treads overhang the outer edge of a stringer one inch. Treads for a deck or porch overhang two inches. Deduct the combined overhang from the width of the stairs, and note the measurement.

4

Make reference marks for the width of the stringers at the horizontal line on the face of the joist. Use a framing square to mark vertical lines on the face of the joist at each reference mark that defines the outer edges of both stringers.

5

Deduct the combined thickness of both stringers to determine the length of a spacer block that installs between the upper ends of the stringers. Typical 2-inch framing lumber used for stringers is 1 1/2 inches thick. In this case, deduct 3 inches from the width between the vertical marks for the stringers, and note the measurement. Measure and cut a piece of 2-inch by 8-inch framing lumber to length with a circular saw.

6

Position the spacer block flat against the face of the joist and align the upper edge at the horizontal line. Move the block either way, as necessary, so each end is 1 1/2 inches from the corresponding vertical mark for a stringer. Use a framing hammer to attach the block at the face of the joist with pairs of 16-penny framing nails at 6-inch intervals from end to end.

7

Position a stringer at one side of the stair's run with the notches for treads facing up. The upper end is against the face of the joist and the inner edge is against the corresponding end of the spacer block. The lower end rests on the floor or concrete footing. Align the top of the stringer at the upper edge of the block. Attach the stringer to the end of the block with three framing nails evenly spaced in a vertical line. Repeat this step and attach the upper end of the remaining stringer at the opposite end of the block.

8

Position the framing square at the intersection of a stringer and the spacer block. Move the bottom of the stringer, as necessary, so the stringer is exactly perpendicular to the face of the block. Make a reference mark on the floor or concrete at the innermost edge of the stringer at the bottom. Repeat this step and position the bottom of the remaining stringer at the floor or concrete, and make a reference mark at its innermost edge.

9

Measure the distance between the bottom ends of the stringers. Measure and cut a piece of 2-inch by 4-inch pressure-treated framing lumber to length as a sole plate.

10

Place the sole plate flat on the floor or concrete and align its outer edge with the outer ends of the stringers. Attach the plate to the floor with framing nails at 4-inch intervals from end to end. For concrete, drill 1/2-inch diameter holes through the plate and 2 inches into the concrete at 4-inch intervals with a power drill and 1/2-inch carbide drill bit. Secure the plate with 1/2-inch by 4-inch expanding anchor bolts at each hole. Tighten the nuts on each bolt with an adjustable wrench.

11

Nail the bottom of each stringer to the corresponding end of the sole plate with a pair of framing nails at each stringer. The stairs are ready for the treads to be installed.

Things You Will Need

Measuring tape

Stair tread

Stepladder

Carpenter’s pencil

4-foot level

Framing square

2-inch by 8-inch framing lumber

Circular saw

16-penny framing nails

Framing hammer

2-inch by 6-inch pressure-treated lumber

Power drill

1/2-inch carbide drill bit

1/2-inch by 4-inch expanding anchor bolts

Adjustable wrench

Tip

Always check the first, or lowest notch for a tread with the level before attaching the bottom of the stringers to the sole plate. Shim up a stringer, if necessary, so the tread will be level.

For stairs along a wall, start by installing a stringer against the face of the wall with three framing nails at each stud. Next, install the spacer block at the face of the joist, and attach the outermost stringer at the outer end of the block.

As an added measure, install 2-inch by 4-inch metal framing angles at the inside corners where the stringers butt against the spacer blocks. Attach these with 1-inch hanger nails at each of the machined holes in the metal angles before installing the treads.

Warning

About the Author

William Machin began work in construction at the age of 15, while still in high school. In 35 years, he's gained expertise in all phases of residential construction, retrofit and remodeling. His hobbies include horses, motorcycles, road racing and sport fishing. He studied architecture at Taft Junior College.